Abutment

ABSTRACT

The present invention relates to an abutment of a dental implant system for connecting a dental implant and a supra-structure, said abutment comprising an abutment basic body extending from an apical end to a coronal end arranged opposite to the apical end. The abutment basic body comprises a dental implant connecting portion facing the apical end and adapted to fit with a corresponding abutment connecting portion of the dental implant and/or an intermediate part to be directly or indirectly connected with the dental implant. It further comprises a support portion facing the coronal end and designed such to allow the suprastructure to be mounted directly or indirectly. According to the invention, the abutment further comprises nanostructures formed on at least a portion of the outer surface of the abutment basic body, said nanostructures extending in at least two dimensions to 200 nm at most.

The present invention relates to an abutment of a dental implant systemfor connecting a dental implant and a suprastructure as well as to aprocess for providing sites of improved protein adherence on an abutmentbasic body.

Dental implants are well known in the art. Generally, they comprise ananchoring part intended to be anchored in a patient's jaw bone and ahead part intended to form the basis on which a suprastructure, such asa bridge or crown, is mounted. The mounting of the suprastructure isthereby often performed by using an intermediate, i.e. a so-called“abutment” (also referred to as “secondary part”), as it is the case ina “two-part implant system” or “multi-part implant system”.

Apart from being biocompatible and having sufficient mechanicalstrength, it is required that the implant provides goodosteointegration.

The term “osteointegration” designates the direct structural andfunctional connection between living bone and the surface of theimplant. A good osteointegration means that the implant, after reachinga primary stability by screwing it into the bone, safely ossifies withina short healing time so that a permanent bond between implant and boneis obtained.

In the past, much effort has been made in order to improve theosteointegrative properties of implants.

Besides the importance of the implant's osteointegrative properties,there is on-growing evidence that also a good interaction between theimplant system and the surrounding supracrestal connective tissue (inthe following referred to as the “soft tissue”) is crucial for asuccessful implantation. This is supported by the view that the softtissue plays a fundamental role in establishing an effective sealbetween the oral environment and the endosseous part of a dental implantand, thus, also a barrier for bacteria to adhere on the soft tissuecontact surface and the bone tissue contact surface of the implantsystem.

Indeed, the presence of bacteria on the implant system's surface maylead to an inflammation of the peri-implant mucosa, and, if leftuntreated, the inflammation spreads apically and results in boneresorption.

As a consequence of the theory that rough surfaces accumulate and retainmore plaque than smooth surfaces (see Oral Implantology, Thieme Verlag,1996, page 438), nowadays, at least the part of the implant system'ssurface, which comes into contact with the soft tissue, is typicallymachined.

As mentioned above, the soft tissue contact surface of the implantsystem would ideally not only provide a surface showing a low tendencyfor bacteria to adhere, but also allow a relatively strong and fastinteraction between the soft tissue and the implant to be established(also referred to as “soft tissue integration”), in order to quicklyprovide an effective seal between the oral environment and theendosseous part.

This applies not only to the dental implant itself, but also to theabutment of a respective dental implant system.

Aiming at an improved soft tissue integration of the implant system,EP-A-2161000 suggests an abutment comprising a soft tissue contactsurface that is at least partially hydroxylated. In this context,improved soft tissue integration is explained by the loose connectivetissue to become organized and replaced be newly formed collagen fibers.

Irrespective of the beneficial effects achieved by the technologydescribed in EP-A-2161000, there is an on-going need for further, simplesolutions for improving soft tissue integration of the abutment, andultimately the dental implant system.

The object of the present invention is thus to provide an abutment theouter surface of which establishes a good soft tissue integration, i.e.a relatively strong interaction between abutment and soft tissue in arelatively timely manner, and which at the same time shows a lowtendency for bacteria to adhere.

This problem is solved by the subject matter of claim 1. Preferredembodiments of the invention are subject of the dependent claims.

According to claim 1, the present invention relates to a abutmentcomprising an abutment basic body extending from an apical end to acoronal end arranged opposite to the apical end, the abutment comprisinga dental implant connecting portion facing the apical end and adapted tofit with a corresponding abutment connecting portion of the dentalimplant and/or an intermediate part to be directly or indirectlyconnected with the dental implant.

The abutment further comprises a support portion facing the coronal enddesigned such to allow the suprastructure to be mounted directly orindirectly, i.e. using at least one intermediate, as it is the case inmulti-part dental implant systems.

According to the invention, the abutment comprises nanostructures formedon the outer surface of the abutment basic body, said nanostructuresextending in at least two dimensions to 200 nm at most.

Preferably, the nanostructures are formed on the outer surface of a softtissue contact region of the abutment basic body, said region beingarranged between the dental implant connecting portion and the supportportion of the abutment basic body. The outer surface of the soft tissuecontact region is in the following also referred to as “soft tissuecontact surface”.

The nanostructures form retention sites, allowing for an improvedinitial adherence of proteins of the cells of the surrounding softtissue. Without wanting to be bound by the theory, transmembraneproteins, specifically integrins, can directly or indirectly, i.e. bymediation of other proteins, adhere to the nanostructures and, thus,establish an anchorage of the cells to the abutment's soft tissuecontact surface. In this complex mechanism, laminins, which is linkedwith the extracellular domain of the integrins, can also play animportant role, as well as plasma proteins, such as albumin, fibrinogenand fibronectin.

Ultimately, the nanostructures forming retention sites allow for anoptimal soft tissue interaction of the abutment and, consequently, aneffective seal between the dental implant system's endosseous part andthe oral environment to be achieved.

According to a particularly preferred embodiment, the outer surface ofthe abutment basic body on which the nanostructures are formed issmooth, e.g. machined or polished.

In other words, the surface topography is smooth when regarded inmacroscopic and microscopic scale, but nevertheless provides ananoscopic structure due to the presence of the nanostructures. Thesenanostructures are small enough not to interfere with the low plaqueforming tendency of the soft tissue contact surface, but big enough toallow proteins of the surrounding soft tissue cells to adhere. As aresult, the soft tissue contact surface's tendency for adherence ofbacteria is low, while at the same time protein adherence of thesurrounding soft tissue cells can take place.

Alternatively to the outer surface of the abutment basic body beingsmooth, it can also be minimally rough, i.e. having a roughness as e.g.obtainable by acid etching.

The term “dental implant” as used in the context of the presentinvention relates to the primary part of a dental implant system, i.e.the part that is actually implanted in the bone, whereas the term“abutment” relates to the “secondary part” of the dental implant system.The term “suprastructure” relates to the prosthetic element of thedental restoration, and in particular relates to a crown or bridge.

In that the outer surface of the abutment basic body on which thenanostructures are formed, in particularly the soft tissue contactsurface, is preferably smooth, it is in clear distinction from the bonetissue contact surface of the dental implant, which typically comprisesa macroscopic topography, achieved e.g. by sand-blasting and/ormachining, as well as a microscopic topography, achieved e.g. by acidetching.

It is understood that the present invention encompasses abutments inwhich nanostructures are formed on the soft tissue contact surface only,as well as embodiments in which they are formed on the surface ofadditional regions than the soft tissue contact region, and embodimentsin which they are formed on the whole surface of the abutment basicbody.

According to a further preferred embodiment, the nanostructures are atleast predominantly in crystalline phase. More preferably, thenanostructures are in an at least approximately purely crystallinephase.

The nanostructures can have different shapes including a needle-likeshape, a leaf-like shape, a flower-like shape, a sphere-like shape or anodule-like shape.

In the context of the present invention, the term “needle-like shape”encompasses any shape having a length to diameter ratio of more than1:1. Thereby, the diameter is to be understood as the expansion of thenanostructure in a direction perpendicular to the longitudinaldirection.

Preferably, the nanostructures have an average length-to-diameter ratioof more than 1 to 1, more preferably of at least 1.5 to 1, mostparticularly ranging from 1.5 to 1 to 4 to 1.

As mentioned, the nanostructures according to the present inventionpreferably extend in at least two dimensions to 200 nm at most. Morespecifically, the nanostructures preferably have an average diameter ofabout 10 nm to 150 nm and an average length of about 5 nm to 500 nm.

It has further been found that by the presence of nanostructures, arelatively high hydrophilicity of the abutment's surface can beachieved, which can further contribute to a good soft tissueinteraction. According to a preferred embodiment, at least a part of thesurface of the abutment, thus, has a hydrophilicity defined by a contactangle of less than 90°, more preferably less than 30°, most preferablyless than 10°, when contacted with water.

It is further preferred that the abutment basic body is made of titaniumor a titanium alloy. A respective basic body allows nanostructures to beformed on its surface in a relatively simple and reproducible manner, aswill be shown below.

In view of its use in the field of implantology, and in particular oralimplantology, any suitable grade of titanium or titanium alloy known tothe skilled person can be used, including titanium of grade 2 to grade4.

When using a titanium alloy, this is preferably a titanium zirconium(TiZr) alloy, typically comprising Zr in an amount of 13 to 17%.Alternatively, a titanium aluminium vanadium alloy, specificallyTi-6Al-4V (TAV), or a titanium aluminium niobium alloy, specificallyTi-6Al-7Nb (TAN), can be used as a titanium alloy suitable for thepurpose of the present invention.

With regard to the use of titanium or a titanium alloy for the abutmentbasic body, it is further preferred that the nanostructures comprisetitanium hydride and/or titanium oxide.

In case the nanostructures comprise titanium hydride, they typicallycomprise TiH₂, whereas in case the nanostructures comprise titaniumoxide, they typically comprise TiO₂.

According to a further aspect, the present invention also relates to aprocess for providing sites of improved protein adherence on an abutmentbasic body, as described above.

According to this process, the nanostructures are grown on the outersurface of the abutment basic body by treating the outer surface of theabutment basic body with an aqueous solution.

The feature that the nanostructures are grown means that they are notformed by a mechanical removing process or by subjecting the surface ofthe body to other mechanical structuring processes. Rather, theformation of the nanostructures occurs gradually in that they “build up”over time by treating the outer surface of the abutment basic body withthe aqueous solution.

The term “aqueous solution” as used in the context of the presentinvention encompasses both pure water as well as a solution in which thesolvent is water.

A particularly good formation/growing of nanostructures has beenobserved for embodiments in which the aqueous solution is an acidicsolution comprising at least one component selected from the groupconsisting of hydrogen fluoride, nitric acid, hydrochloric acid,sulphuric acid, tartaric acid, oxalic acid, citric acid and acetic acid,and/or mixtures thereof.

As mentioned above, the abutment basic body is typically made oftitanium or a titanium alloy.

According to a well-controllable and thus preferred process, the growingof the nanostructures is performed by cathodic polarization (alsoreferred to as “cathodic hydridation”), in which the abutment basic bodyforms the cathode. A detailed description of this process will be givenby way of the examples below.

In this regard, it is particularly preferred that before performingcathodic polarization, at least a portion of the outer surface of theabutment basic body is pickled with a pickling solution in order to atleast partially remove a titanium oxide layer present on the outersurface. A pickling solution comprising at least one component selectedfrom the group consisting of nitric acid, hydrofluoric acid, ammoniumfluoride, hydrochloric acid and sulphuric acid, and/or mixtures thereof,particularly a mixture of nitric acid and hydrofluoric acid, is therebypreferably used.

With regard to the cathodic polarization, this is preferably performedin a buffer having a pH in the range from 0 to 6. The temperature ispreferably set in a range from 5 to 95° C., preferably from 10 to 75°C., more preferably from 15 to 50° C., most preferably at about roomtemperature.

Additionally or alternatively to the above described process usingcathodic polarization, the nanostructures can be grown on the outersurface of the abutment basic body by storing the outer surface of theabutment basic body in the aqueous solution.

The storing is typically carried out by using a 0.9% NaCl solution, morespecifically having a pH of 2 to 7, preferably 3 to 6. Likewise, anyother suitable aqueous solution can be used including pure water.

According to a particularly preferred embodiment, the storing is carriedout for at least one month, more preferably at least two months, mostpreferably at least four months. The storage time depends on the surfacetopography of the outer surface of the abutment basic body. For amachined surface, the storage times required for the growing of thenanostructures has been found to be longer than for a rough surface.However, also for a machined surface, nanostructures are detected aftertwo months of storing.

With regard to the storing, it is further preferred that this isperformed at an elevated temperature, i.e. a temperature above roomtemperature, since nanostructure formation has been shown to beparticularly pronounced at these temperatures.

A temperature in a range of about 50° C. to 250° C., more particularlyabout 100° C. to 180° C., and most preferably about 120° C. to 150° C.has been shown to be particularly preferred, since the storing timerequired for the growing of nanostructures can be shortenedsubstantially. A storing over months is, thus, not required whenperforming a (hydro-)thermal treatment at the temperatures specifiedabove.

It is understood that the process of the present invention encompassesembodiments in which only the soft tissue contact region is subjected tothe treatment with the aqueous solution, as well as embodiments in whichadditional regions and embodiments in which the whole surface are/issubjected to this treatment.

As mentioned, embodiments in which the outer surface of the abutmentbasic body on which the nanostructures are formed is smooth, preferablymachined or polished. Depending on the actual aim to be achieved,alternative embodiments can be preferred, in which the outer surface ofthe abutment basic body on which the nanostructures are formed is rough.This is due to the finding that nanostructure formation has been shownto be favoured on a roughened surface.

The present invention is further exemplified by way of the followingexamples:

EXAMPLES Treatment of the Samples

Titanium samples were grinded and polished and were then washed withNaOH at 40% (w/v) and HNO₃ at 40% (w/v) in an ultrasonic bath to removecontaminants, then washed with deionized water to reach a neutral pH andstored at room temperature in 70 vol.-% ethanol.

After the polishing and cleaning steps, some of the samples were treated(“pickled”) for one minute in a solution containing 15 wt.-% HNO₃ and 5wt.-% HF (solution C1) at room temperature (samples p1). Alternatively,samples were treated in a solution C1 diluted twice with deionized water(samples p2), diluted five times with deionized water (samples p5) anddiluted ten times with deionized water (samples p10).

Immediately after the pickling treatment, the samples were washed bydipping in a beaker containing deionized water for 10 seconds, thenmounted on a sample holder forming a cathode for cathodic polarization(or cathodic hydridation).

For the cathodic hydridation, current densities at 5, 10 and 15 mA/cm2were used. The hydration was performed at room temperature and theduration of the hydridation was set to 0.5, 2 and 5 hours. Aselectrolyte, tartaric acid at 1 M of concentration, pH 1.9, was used.

Nanoscale Analysis of the Samples

Following the hydridation step, a nanoscale analysis of each of themodified surfaces was performed using a Field Emission Scanning ElectronMicroscope (FE-SEM; Quanta 200F, FEI, The Netherlands).

Thereby, nanostructures, in the particular case nano-nodules, with adiameter well below 200 nm were detected as white “spots”. Thesenanostructures form retention sites for improved protein adherence ofthe surrounding soft tissue.

1. Abutment of a dental implant system for connecting a dental implantand a suprastructure, said abutment comprising an abutment basic bodyextending from an apical end to a coronal end arranged opposite to theapical end, the abutment basic body comprising a dental implantconnecting portion facing the apical end and adapted to fit with acorresponding abutment connecting portion of the dental implant and/oran intermediate part to be directly or indirectly connected with thedental implant and further comprising a support portion facing thecoronal end and designed such to allow the suprastructure to be mounteddirectly or indirectly, wherein the abutment further comprisesnanostructures formed on at least a portion of the outer surface of theabutment basic body, said nanostructures extending in at least twodimensions to 200 nm at most.
 2. Abutment according to claim 1, whereinnanostructures are formed on the outer surface of a soft tissue contactregion of the abutment basic body, said region being arranged betweenthe dental implant connecting portion and the support portion of theabutment basic body.
 3. Abutment according to claim 1, wherein the outersurface of the abutment basic body on which the nanostructures areformed is smooth, preferably machined or polished.
 4. Abutment accordingto claim 1, wherein the outer surface of the abutment basic body onwhich the nanostructures are formed is minimally rough.
 5. Abutmentaccording to claim 1, wherein the abutment basic body is made oftitanium or a titanium alloy.
 6. Abutment according to claim 1, whereinsaid nanostructures comprise titanium hydride, particularly TiH₂, and/ortitanium oxide, particularly TiO₂.
 7. Abutment according to claim 1,wherein the nanostructures are at least predominantly in crystallinephase.
 8. Abutment according to claim 1, wherein the nanostructures havean average length-to-diameter ratio of more than 1 to 1, preferably ofat least 1.5 to 1, and more preferably ranging from 1.5 to 1 to 4 to 1.9. Abutment according to claim 1, wherein the nanostructures have anaverage diameter of about 10 nm to 150 nm and an average length of about5 nm to 500 nm.
 10. Abutment according to claim 1, wherein at least apart of the surface of the abutment has a hydrophilicity defined by acontact angle of less than 90°, more preferably less than 30°, mostpreferably less than 10°, when contacted with water.
 11. Process forproviding sites of improved protein adherence on an abutment basic body,wherein nanostructures are grown on the outer surface of the abutmentbasic body by treating it with an aqueous solution.
 12. Processaccording to claim 11, wherein the abutment basic body is made oftitanium or a titanium alloy.
 13. Process according to wherein claim 11,wherein the aqueous solution is an acidic solution comprising at leastone component selected from the group consisting of hydrogen fluoride,nitric acid, hydrochloric acid, sulphuric acid, tartaric acid, oxalicacid, citric acid and acetic acid, and/or mixtures thereof.
 14. Processaccording to claim 11, wherein the growing of the nanostructures isperformed by cathodic polarization, in which the abutment basic bodyforms the cathode.
 15. Process according to claim 14, wherein beforeperforming cathodic polarization at least a portion of the outer surfaceof the abutment basic body is pickled with a pickling solution in orderto at least partially remove a titanium oxide layer present on the outersurface.
 16. Process according to claim 15, wherein the picklingsolution comprises at least one component selected from the groupconsisting of nitric acid, hydrofluoric acid, ammonium fluoride,hydrochloric acid and sulphuric acid, and/or mixtures thereof,particularly a mixture of nitric acid and hydrofluoric acid.
 17. Processaccording to claim 14, wherein cathodic polarization is performed in abuffer having a pH in the range from 0 to
 6. 18. Process according toclaim 14, wherein cathodic polarization is performed at a temperature ina range from 5 to 95° C., preferably from 10 to 75° C., more preferablyfrom 15 to 50° C., most preferably at about room temperature. 19.Process according to claim 11, wherein nanostructures are grown on theouter surface of the abutment basic body by storing it in the aqueoussolution.
 20. Process according to claim 19, wherein the storing isperformed for at least one month, more preferably at least two months,most preferably at least four months.
 21. Process according to claim 19,wherein the storing is performed above room temperature, in particularat a temperature in a range of 50° C. to 250° C., more particularly 100°C. to 180° C., and most preferably about 120° C. to 150° C.